﻿using System;
using System.Collections.Generic;
using System.Text;

namespace lmsft.Media.Codec.Audio
{
	/// <summary>
	/// Implements PCMU(G711 ulaw) codec.
	/// </summary>
	public class PCMU : AudioCodec
	{
		#region byte[] MuLawCompressTable

		private static readonly byte[] MuLawCompressTable = new byte[]{
			0,0,1,1,2,2,2,2,3,3,3,3,3,3,3,3,
			4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,
			5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
			5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
			6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
			6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
			6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
			6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
			7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
			7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
			7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
			7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
			7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
			7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
			7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
			7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7
		};

		#endregion

		#region short[] MuLawDecompressTable

		private static readonly short[] MuLawDecompressTable = new short[]{
			-32124,-31100,-30076,-29052,-28028,-27004,-25980,-24956,
			-23932,-22908,-21884,-20860,-19836,-18812,-17788,-16764,
			-15996,-15484,-14972,-14460,-13948,-13436,-12924,-12412,
			-11900,-11388,-10876,-10364, -9852, -9340, -8828, -8316,
			-7932, -7676, -7420, -7164, -6908, -6652, -6396, -6140,
			-5884, -5628, -5372, -5116, -4860, -4604, -4348, -4092,
			-3900, -3772, -3644, -3516, -3388, -3260, -3132, -3004,
			-2876, -2748, -2620, -2492, -2364, -2236, -2108, -1980,
			-1884, -1820, -1756, -1692, -1628, -1564, -1500, -1436,
			-1372, -1308, -1244, -1180, -1116, -1052,  -988,  -924,
			-876,  -844,  -812,  -780,  -748,  -716,  -684,  -652,
			-620,  -588,  -556,  -524,  -492,  -460,  -428,  -396,
			-372,  -356,  -340,  -324,  -308,  -292,  -276,  -260,
			-244,  -228,  -212,  -196,  -180,  -164,  -148,  -132,
			-120,  -112,  -104,   -96,   -88,   -80,   -72,   -64,
			-56,   -48,   -40,   -32,   -24,   -16,    -8,     0,
			32124, 31100, 30076, 29052, 28028, 27004, 25980, 24956,
			23932, 22908, 21884, 20860, 19836, 18812, 17788, 16764,
			15996, 15484, 14972, 14460, 13948, 13436, 12924, 12412,
			11900, 11388, 10876, 10364,  9852,  9340,  8828,  8316,
			7932,  7676,  7420,  7164,  6908,  6652,  6396,  6140,
			5884,  5628,  5372,  5116,  4860,  4604,  4348,  4092,
			3900,  3772,  3644,  3516,  3388,  3260,  3132,  3004,
			2876,  2748,  2620,  2492,  2364,  2236,  2108,  1980,
			1884,  1820,  1756,  1692,  1628,  1564,  1500,  1436,
			1372,  1308,  1244,  1180,  1116,  1052,   988,   924,
			876,   844,   812,   780,   748,   716,   684,   652,
			620,   588,   556,   524,   492,   460,   428,   396,
			372,   356,   340,   324,   308,   292,   276,   260,
			244,   228,   212,   196,   180,   164,   148,   132,
			120,   112,   104,    96,    88,    80,    72,    64,
			56,    48,    40,    32,    24,    16,     8,     0
		};

		#endregion

		private AudioFormat m_pAudioFormat = new AudioFormat(8000, 16, 1);
		private AudioFormat m_pCompressedAudioFormat = new AudioFormat(8000, 8, 1);

		/// <summary>
		/// Default constructor.
		/// </summary>
		public PCMU() {
		}


		#region method Encode

		/// <summary>
		/// Encodes linear 16-bit linear PCM to 8-bit ulaw.
		/// </summary>
		/// <param name="buffer">Data to encode. Data must be in Little-Endian format.</param>
		/// <param name="offset">Offset in the buffer.</param>
		/// <param name="count">Number of bytes to encode.</param>
		/// <returns>Returns encoded block.</returns>
		/// <exception cref="ArgumentNullException">Is raised when <b>buffer</b> is null reference value.</exception>
		/// <exception cref="ArgumentException">Is raised when any of the arguments has invalid value.</exception>
		public override byte[] Encode(byte[] buffer, int offset, int count) {
			if (buffer == null) {
				throw new ArgumentNullException("buffer");
			}
			if (offset < 0 || offset > buffer.Length) {
				throw new ArgumentException("Argument 'offset' is out of range.");
			}
			if (count < 1 || (count + offset) > buffer.Length) {
				throw new ArgumentException("Argument 'count' is out of range.");
			}
			if ((count % 2) != 0) {
				throw new ArgumentException("Invalid buffer value, it doesn't contain 16-bit boundaries.");
			}

			var offsetInRetVal = 0;
			var retVal = new byte[count / 2];
			while (offsetInRetVal < retVal.Length) {
				// Little-Endian - lower byte,higer byte.
				var pcm = (short)(buffer[offset + 1] << 8 | buffer[offset]);
				offset += 2;

				retVal[offsetInRetVal++] = LinearToMuLawSample(pcm);
			}

			return retVal;
		}

		#endregion

		#region method Decode

		/// <summary>
		/// Decodes 8-bit ulaw to linear 16-bit PCM.
		/// </summary>
		/// <param name="buffer">Data to decode. Data must be in Little-Endian format.</param>
		/// <param name="offset">Offset in the buffer.</param>
		/// <param name="count">Number of bytes to decode.</param>
		/// <returns>Returns decoded data.</returns>
		/// <exception cref="ArgumentNullException">Is riased when <b>buffer</b> is null reference value.</exception>
		/// <exception cref="ArgumentException">Is raised when any of the arguments has invalid value.</exception>
		public override byte[] Decode(byte[] buffer, int offset, int count) {
			if (buffer == null) {
				throw new ArgumentNullException("buffer");
			}
			if (offset < 0 || offset > buffer.Length) {
				throw new ArgumentException("Argument 'offset' is out of range.");
			}
			if (count < 1 || (count + offset) > buffer.Length) {
				throw new ArgumentException("Argument 'count' is out of range.");
			}

			var offsetInRetVal = 0;
			var retVal = new byte[count * 2];
			for (var i = offset; i < buffer.Length; i++) {
				var pcm = MuLawDecompressTable[buffer[i]];
				retVal[offsetInRetVal++] = (byte)(pcm & 0xFF);
				retVal[offsetInRetVal++] = (byte)(pcm >> 8 & 0xFF);
			}

			return retVal;
		}

		#endregion


		#region static method LinearToMuLawSample

		private static byte LinearToMuLawSample(short sample) {
			var cBias = 0x84;
			var cClip = 32635;

			var sign = (sample >> 8) & 0x80;
			if (sign != 0) {
				sample = (short)-sample;
			}
			if (sample > cClip) {
				sample = (short)cClip;
			}
			sample = (short)(sample + cBias);
			var exponent = (int)MuLawCompressTable[(sample >> 7) & 0xFF];
			var mantissa = (sample >> (exponent + 3)) & 0x0F;
			var compressedByte = ~(sign | (exponent << 4) | mantissa);

			return (byte)compressedByte;
		}

		#endregion


		#region Properties implementation

		/// <summary>
		/// Gets codec name.
		/// </summary>
		public override string Name {
			get { return "PCMU"; }
		}

		/// <summary>
		/// Gets uncompressed audio format info.
		/// </summary>
		public override AudioFormat AudioFormat {
			get { return m_pAudioFormat; }
		}

		/// <summary>
		/// Gets compressed audio format info.
		/// </summary>
		public override AudioFormat CompressedAudioFormat {
			get { return m_pCompressedAudioFormat; }
		}

		#endregion

	}
}
